PHSI 208 Lecture Notes - Brainstem, Central Canal, Vasodilation
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STRUCTURE AND FUNTION OF THE HUMAN BRAIN BOX
inside the skull the brain is enveloped within three layers of non neural tissue, membranes referred to as meninges
viewed from the top the brain is divided by a midline fissure into two mirror image cerebral hemispheres together
constituting most of the cerebrum.
The cerebrum is the thinking centre of the brain, which includes the cortex and sub cortex structures such as the
basal ganglia and limbic system.
The major connections between the two hemispheres is a band of nerve fibres called the corpus callosum
The upper side and some of the lower surfaces of the hemispheres form the cerebral cortex
The corxt consist of 6 layers of tiglhy packed neuron cell bodies with many short unsheathed interconnecting
These neurons estimated to # 10-15 billion make up a thin outer covering the so called grey matter of the brain
The cortex is vastly convoluted; the ridges are called gyri and the depressions between them suici, several distinct
areas called lobes
The frontal lobe lies in front of the central suclus, the parietal lobe is behind it and above the later suclus , the
temporal lobe is located below the lateral suclus and the occipital love lies behind the parietal and temporal lobes
Vision in the occipital; discrimination of sounds in the temporal; reasoning and other higher mental processes as
well as the regulation of fine voluntary movement in the frontal; initiation of movements of the skeletal
musculature in a band in front of the central sulcus; and receipt of sensations of touch, pressure, pain,
temperature and body position from skin, muscles, tendons, and joints in a band behind the central sulcus
The two hemispheres of the brain have different functions. The left hemisphere which generally controls the right
half of the body cuz of the crossing over of motor and sensory fibres is responsible for speech and according to
some neuropsychologists for analytical thinking in right handed ppl and in a fair # of left handed ppl as well
The right hemisphere controls the left side of the body, discerns spatial relations and patterns and is involved in
emotion and intuition
The two hemispheres communicate with each other constantly via the corpus callosum
The grey matter of the cerebral cortex does not extend throughout the interior of the brain.
Much of the interior is white matter made up of large tracts or bundles or myelinated (sheathed) fibres that
connect cell bodies in the cortex with those in the spinal cord and other centres lower in the brain
These centres are pockets of grey matter referred to as nuclei. The nuclei serve both as way stations connecting
tracts from the cortex with other ascending and descending tracts and as integrating motor and sensory control
Some cortical cells project their long fibres or axons to motor neurons in the spinal cord but others project them
only as far as these clusters of interconnecting neuron cell bodies.
Four masses are deep within each hemisphere called collectively the basal ganglia. Also deep within the brain are
cavities called ventricles; those are continuo’s with the central canal of the spinal cord and are filled with
1) The diencephalons connected in the front of the hemispheres and behind with the midbrain contains the
thalamus and the hypothalamus both consisting of groups of nuclei. The thalamus is a relay station for all sensory
pathways except the olfactory. The nuclei making up the thalamus receive nearly all the impulse arriving from the
different sensory areas of the body and then pass tem on to the cerebrum where they are interpreted as conscious
sensations. The hypothalamus is the highest centre of integration for many visceral processes, regulating
metabolism, temperature, perspiration, blood pressure, sleeping and appetite
2) The midbrain is a mass nerve fibre tracts connecting the cerebral cortex with the pons, the medulla oblongata,
the cerebellum and the spinal cord
3) The brain stem comprises the pons and the medulla oblongata and functions primarily as a neural relay station.
The pons contains tracts that connect the cerebellum with the spinal cord and with motor areas of the cerebrum.
The medulla oblongata serves as the main line of traffic for tracts asceing from the spinal cord and desceing from
the higher centres of the brain. At the bottom of the medulla, many of the motor fibres cross to the opposite side.
The medulla also contains nuclei that maintain the regular life rhythms of the heartbeat of the rising and falling
diaphragm and of the constricting and dilating blood vessels. In the core of the brain stem is the reticular
formation sometimes called the reticular activating system cuz of the important role it pays in arousal and connect